If you think about the legal requirements for a NP, I can't see any reason why they couldn't allocate such a small site (there is similarly no legal threshold for local plans) - it is more a matter of effort vs reward! Unless there is something in the local plan strategic policies that would go against the specifics of that site (eg if it were a residential garden and there was a strategic policy on graden grabbing). I'm assuming the site is outside a settlement boundary? If it is it may of course become more obsolete if the NPPF changes on small sites adjoining settlement boundaries comes into play.
Jo
